This proposal has as its basic theme the isolation and characterization of the protein phosphatase(s) involved in the interconversion of the enzymes of glycogen metabolism, and the elucidation of the mechanisms of their control of protein functions via phosphorylation-dephosphorylation mechanisms. The study will be centered around the isolation of phosphorylase phosphatase in a high molecular weight form. Current evidence indicates that this is the native enzyme form which may be a holoenzyme which contains a catalytic subunit of molecular weight 35,000, as well as putative regulatory subunits. The subunit structure of the holoenzyme will be determined, and the function of the putative regulatory subunits will be established. The properties of the holoenzyme will be examined in terms of potential regulatory mechanisms. The specificity of the holoenzyme and its catalytic subunits will be examined in terms of their activity on phosphorylase kinase and glycogen synthase. The question of whether the holoenzyme isolated as a phosphorylase phosphatase also represents the major protein phosphatase activity in tissues toward phosphorylase kinase and glycogen synthase will be investigated. The effects of protein inhibitors on the isolated phosphatases will be investigated. Studies of the Mr 35,000 species of protein phosphatase will be extended in terms of the characterization of its properties and in terms of the characterization of a presumptive membrane-bound form. Levels of protein phosphatase activity in the liver of normal and diabetic rats, and the possible inactivation or loss of one of these activities in the diabetic state will be examined. The effect of insulin in restoring or reactivating protein phosphatase activities in the diabetic rat will also be studied.